A distinguishing feature of lentiviruses such as HIV-1 is their ability to infect nondividing cells. We and others have demonstrated that this property of HIV-1 is governed by the ability of the reverse transcription complex to translocate to the host cell nucleus in the absence of mitosis. We have previously suggested a model in which nucleophilic virion components remain associated with the reverse transcription complex to facilitate its nuclear localization. Three virion proteins have been implicated in this process, namely gag MA, integrase and Vpr. The association of HIV-1 gag MA with the reverse transcription complex creates a paradox. During virus assembly, gag MA is cotranslationally myristoylated and this promotes membrane targeting of gag polyproteins to the plasma membrane. We have recently demonstrated that the membrane targeting properties of gag MA are regulated by phosphorylation which, in a newly infected cell, promotes membrane detachment of gag MA, thus, allowing free translocation of the reverse transcription complex from the point of virus entry to the host cell nucleus. Thus, gag MA phosphorylation represents a central event which governs HIV-1 infectivity. We have now extended upon these initial observations in the first phase of the AIDS-FIRCA application by characterizing a kinase which is virion associated, which phosphorylates gag MA and which modulates HIV-1 infectivity. Furthermore, we have demonstrated that establishment of a functional reverse transcription complex within the infected cell requires interaction with actin microfilaments of the host cell cytoskeleton. The object of this competing AIDS-FIRCA application is to examine how gag MA phosphorylation influences cytoskeletal interaction of the reverse transcription complex and the ability of the complex to promote reverse transcription of genomic viral RNA. The aims to be undertaken include: Aim 1: Define the role of gag MA phosphorylation in mediating interaction between the viral reverse transcription complex and the host cell cytoskeleton in vitro and in vivo. Aim 2: Examine how cytoskeltal engagement influences the reverse transcription capacity of the reverse transcription complex and how this dependence is influenced by gag MA phosphorylation.